Transmission control in two-way signaling systems



Aug. 29, 1944; A. c. NoRwlNE TRANSMISSION CONTROL IN TWO-WAY SIGNALING SYSTEMS 'Filed Aug. 29, 1942 ATTORNEY E RW H M Il lv w. MR A w it N l /c f S Aw TQ M A .IV E# In lv Y www( V. Cum B @mi ix K9. Q Li L ko .uw xvtm f E S T Q EN@ E E j vN\ Yum Q Q D.v\ i: Gum EAU iw l E l mf. www m. n W AV N N\ mw Aw Il 4 .@xmm EN QL y A Patented Aug. 29, '1944 TRANSMISSION CONTROL IN TWO-WAY SIGNALING SYSTEMS Andrew C. Norwine, Short Hills, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application August 29, 1942, Serial No. 456,605

4 Claims.

The invention relates to two-way signal transmission systems and particularly to the signalcontrolled switching circuits used with such systems to directionally control signal transmission i therein while suppressing echoes and preventing singing.

switching branch, so as to provide theA desired directional control of signal transmission while suppressing echoes and preventing singing.

' The prior patent application of Norwine and Davis, Serial No. 421,704,1led `December 5, 1941, which issued as Patent 2,306,689 on December 29, 1942, discloses in combination with such an echo suppressor applied to a four-wire telephone circuit, break-in control circuits operating onY an amplitude basis. 'These circuits enable one subscriber to break in on another who is talking and has operated his echo suppressor switching controls to seize directional control of the system, without waiting for the latter to pause and regardless of how loudly the latter is talking. This is accomplished by the use of other relatively insensitive controls respectively connected to each side of the four-wire circuit in front of the disabling point therein, operating in response to applied voice signals of a level a given amount greater than normal level to immediately disable the echo suppressor switching branch controlled from the other side ofthe four-wire circuit.

An object of the invention is to improve the operation of such break-in echo suppressor circuits.

A more speciiic object is to prevent speech signal mutilation in an echo suppressor equipped with a break-in control ofthe vamplitude type, due to rapidly repeated interruptions ofthe two talkers by each other, l Y

These objects areaccomplished in accordance withV the invention by making the amplitude break-in controls normally inoperative and providing auxiliary controls for causing each breakin control to be enabled a predetermined time after operation of the echo suppressor branch which it is to disable, to provide break-in.

The various objects and features of the invention will be better understood from the following detailed description when read in conjunction with the accompanying drawing, the single figure of which shows schematically a four-wire telephone circuit equipped with an echo suppressor embodying the invention.

In the iigure, the four-wire telephone circuit of the drawing includes a one-way, two-wire transmission path EA including the amplifiers A1 and A2, normally conditioned to transmit in the direction from west to east between the two-way line LW and the two-way line LE; and the one-way, two-wire transmission path WA including the amplifiers A3 and A4, normally conditioned to transmit in the direction from east to west between the two-Way line LE and the two-way line LW. The transmission paths EA and WA are coupled at the west and east terminals of the four-wire circuit, in conjugate relation with each other and in energy transmitting relation with the lines LW andLE by the hybrid coil Hw and associated balancing network Nw, and the hybrid coil HE and associated balancing net- Work NE, respectively.

Connected across the west to east path EA at an ,intermediate point I is the input of a voicecontrolled echo suppressor branch circuit 2, to be referred to hereinafter as the west echo suppressor,inc1uding the wave-controlled control device (amplier-rectier) 3 and the electromagnetic switching relay 4 adapted to be operatively energized by the rectied signal output of the device 3. Similarly, connected across the east to West path WA at an intermediate point 5 is the input of a voice-controlled echo suppressor branch circuit 6, to be referred to hereinafter as the east echo suppressor, including the wave controlled control device (amplifier-rechner) 1, and the electromagnetic switching relay 8 adapted to be operatively energized by the rectied signal output of the device 1. The relay 4 in the west echo suppressor 2, when energized, operates to close a short-circuiting connection across the path WA at the point 9 in front of the point 5 to which the east echo suppressor 6 is connected, to disable that path. Similarly the relay 8 of the east echo suppressor 6, when energized, operates to close a short-circuiting connection across the path EA at the point l0 in front of the point to which the west echo suppressor 2 is connected, to disable that path.

Connected across the west to east transmission path EA at a point II in front of the disabling point I Il is the input of a third control circuit I2, to be referred to hereinafter as the west break-in control, which control circuit as indicated by the series resistances in its input, is relatively insensitive as compared with the west echo suppressor 2. The west break-in control I2 includes a wave-operated control device (amplifier-rectifier) I4, and an electromagnetic switching relay I5 which when energized by the detected signal output of the device I4, operates to open its normally closed contacts to disable the east echo suppressor 6 at a" point I6 in its output. The west break-in control I2 is normally disabled at a point between the output of the amplifier-rectifier I4 and the relay I5 by the normally open contacts of switching relay I 3.

Similarly, connected across the east to west transmission path WA at a point II in front of the disabling point 9 is the input of a fourth control circuit I8, to be referred to hereinafter as the east break-in control, which, as indicated by the series resistances in its input, is relatively insensitive compared with the east echo suppressor 6. The east break-in control I8 includes the Wave-operated control device (amplier-rectier) 28, and an electromagnetic relay 2| adapted to be operatively energized by the signal output of the control device 20 to disable the east echo suppressor 2 at the point 22 in its output. The east break-in control I8 is normally disabled at a point between the output of the amplierrectifier 20 and the relay 2| by the normally open contacts of relay I9.

Connected across the west echo suppressor 2 at a point between the disabling point 22 and the output of the amplier-rectier 3 is the input of a fth control circuit 23, to be referred t0 hereinafter as the east break-in control enabler, including the electromagnetic switching relay I9 which when completely energized from the output of amplifier-rectifier 3, operates to close its normally open contacts to enable the east breakin control I8. As indicated by the delay circuit 24 connected between the relay I9 and the output of the amplifier-rectifier 3, the latter relay is given a delay in operation of T seconds with respect to the operation of the west echo suppressor relay 4 also controlled from the output of amplifier-rectifier 3.

Similarly, connected across the output of the east echo suppressor 6 at a point between the disabling point IIS and the output of the amplier-rectier 'I is the input of a sixth control circuit 25, to be referred to hereinafter as the west break-in control enabler, including the electromagnetic switching relay I3 which, when completely energized from the output of the amplier rectifier 1, operates to close its normally open contacts to enable the west break-in control I2. As indicated by the delay circuit 26 connected in the control circuit 25 between relay I3 and the output of the amplifier-rectifier 1, the latter relay is also given a delay in operation of T seconds with respect to that of the east echo suppressor relay 8 also controlled from the output of amplifier-rectifier 1.

Break-in controlenablers 23 and 25 should have the same sensitivities as the echo suppressor branches with which they are associated. Break-in controls I2and I8 should be made as sensitive as they can be without permitting false operation on echoes of speech signals impressed on the respective opposite sides of the circuit.

Let it be assumed that a west telephone subscriber associated with the line LW starts to speak and at that time the east subscriber associated with the line LE is silent. The speech waves of the west subscriber received over the line LW will pass through the hybrid coil Hw to the west to east transmission path EA of the four-wire circuit, and over that path through the hybrid coil HE and the line LE to the east subscriber. A portion of these speech Waves will be diverted at the point I in the path EA into the west echo suppressor 2 causing the operation of the amplifier-rectifier 3 and thus that of the switching relay 4 in its output to disable the east to west |path WA at the point 9. This also effectively disables the east echo suppressor 6 connected to the path WA at the-subsequent point 5. The echoes of Wests speech signals passing into the path WA through hybrid coil HE, as well as subsequently received signals from the east subscriber, will, therefore, be suppressed at the point 9 and prevented. from reaching the input of the east echo suppressor 6 to cause false operation of the latter to reverse directional control of the circuit.

T seconds after the west echo suppressor 2 has thus operated to give directional control of the four-wire circuit to the west talker, the portion of the rectied signals in the outputof the amplier-rectiiier 3 of the west echo suppressor 2 diverted into the east break-in control enabler circuit 23 will have passed through the delay circuit 24 and will cause the operation of the relay I9 to enable the east break-in control I8. Up to this time, the east subscriber associated with the line LE will not be able to interrupt the west subscriber because the east break-in control I8 will be in the disabled condition. However, when the relay I9 finally operates to enable the east break-in control circuit I8, it is possible for the east subscriber to interrupt west immediately by talking loudly enough to overcome the desensitization provided by the series resistancesin the input of east break-in control I8. When east does so, his speech signals diverted into the east break-in control I8 will cause operation of the amplifier-rectifier 20 and thus of the break-in relay 2| to immediately disable the west echo suppressor 2 at the point 22 in its output. The echo suppressor relay 4 will then release to remove the short-circuiting connection across the path WA at the point 9 and thus to interrupt the west subscribers directional control ofthe circuit. The east subscribers speech currents received from the line LE then will pass over the now enabled east to west transmission path WA and through the hybrid coil Hw and line LW to the west subscriber. The portion of easts speech waves diverted from the path WA into the east echo suppressor 6 will cause the operation of the amplifier-rectifier 'I and thus of the echo suppressor relay 8 in its output to close a shortcircuiting connection across the path EA at the point I 0. The echoes of easts speech waves passing into the path EA will therefore be suppressed at the point I0 and speech currents subsequently received from west will be prevented from passing over that path to the east subscriber, as long as east continues to hold his echo suppressor relay 8 operated. T seconds after relay 8 operates, the portion of easts rectified speech currents passing from the output of the amplier-rectier I into the west break-in control enabler branch 25 and delayed in that branch for that time interval by delay circuitA 26 l Waves.

will operate relay I3 to enable the west break-in control I2. At any time thereafter, the west subscriber by talking loudly enough to overcome the desensitization provided by the series resistances in the input of the west break-in control I2 will be able to interrupt the east talker by operating the amplifier-rectifier I4 and thus switching relay I5 to disable the east echo suppressor 6 at the point I6. The consequent release of relay 8 will unblock the path EA, enabling Wests speech currents to'y get through to the east subscriber and to operate the west echo suppressor 2 to regain directional control.

It will be seen from the above description of operation of the system of the drawing that a listener cannot interrupt the talker and obtain directional control of the system until a given time, T seconds, after the first talker starts to talk when the listeners break-in control is enabled under control of the rst talkers speech Thus in the normal course of events, a listener could reply sooner than with a conventional echo suppressor and once successful in breaking in would hold control for a reasonable time without himself being interrupted. With T in the order of, say, half a second, many of the repeated reversals that might otherwise take place should be eliminated, and both talkers should hear more lintelligible interruptions.

To provide break-in that will be intelligible it has been found that break-in relays I5 and 2| should remain operated for a short time after the operating speech energy has ceased. This hangover time should be about one hundred milliseconds. This hangover may be obtained by suitable design of the relays or by the use of associated resistance-condenser hangover circuits. Break-in enabler relays I3 and I9 also should be provided with hangovers, to insure that breakin means are available as much of the time as V possible excluding the time T after a talker starts talking and excluding lookup between successive speeches by the same talker. These hangovers preferably should be in the order of T seconds. Thus if delay 26 is a relay chain terminating in relay I3, the combination should operate in T seconds after speech energy arrives at point 6 and it should release in about T seconds after the speech energy ceases.

Various modications of the circuits. illustrated and described which are within the spirit and scope of the invention will occur to persons skilled in the art.

What is claimed is:

1. In combination in a two-way telephone system including two oppositely directed one-way signal transmission paths, one switching device connected to each path responsive to voice signal transmission therein, in the absence of prior voice signal transmission in the other path, to disable said other path and said one switching device connected thereto, a second relatively insensitive switching device connected to each path in front of the disabling point therein, responsive to voice signal transmission in that path of a level at least a given amount above average level to disable said one switching device connected to the other ond switching devices, and means responsive to voice signal transmission in each path when that path is operative, for enabling the said second switching device connected to the other path a predetermined time after said one switching device connected to the first path has operated to disable said other path.

2. In a two-way telephone transmission systern including oppositely directed one-way transmission paths for transmitting the voice signals in opposite directions, an echo suppressor device connected to veach path, responsive to voice signal `transmission in that path, in the absence of prior voice-signal transmission in the other oneway path, to disable said other path, a normally disabled break-in control circuit connected to each path in front of the disabling point therein, which when operative is responsive to voice signal transmission in that path of a level at least a given amount above average level to disable the echo suppressor device controlled from the other path, and means responsive to voice signal transmission in each path when that path is operative to enable the break-in control circuit connected to the other path a given time after the echo suppressor device controlled from the first path operates in response to that voice signal transmission.

L 3. The Asystem of claim 2 in which said giy e n I time after the echo suppressor device controlled from the first path operates is in the order of one-half of asecond.

4. In combination in a two-way telephone system including two oppositely directed one-way transmission paths for respectively transmitting the voice signals of the subscribers generated at opposite ends of the system, one voice-operated switching device connected to each path, responsive to voice signal transmission over that path to disable the other path and effectively disable said one switching device connected thereto, so as to give directional control of the system to the subscriber who first starts to talk, means to enable break-in by a subscriber at either end of the system when the subscriber at the other end is talking and has obtained directional control of the system, comprising a relatively insensitive break-in control device connected to each path in front of the disabling point therein, operating only in response to applied voice signals of an amplitude level at least a given amount above normal level, to immediately disable the switching device controlled from the other path and means to prevent voice signal mutilation by reversals of directional control due to rapidly repeated interruptions of each other by the'two talking subscribers, comprising means normally disabling each break-in control device and means responsive to operation of the said one switching device connected to each path to enable the break-in control device connected to the other path a given time after said other path has been disabled by,that switching device.

ANDREW C. NORWINE. 

